Silicone rubber is valued for electrical insulation, heat resistance, weather resistance and flame retardance and used, for example, as coatings on fixing rolls like heating rolls and pressure rolls in copiers and laser printers. To comply with higher speed copiers and color copiers which are recently on wide-spreading use, fixing rolls are required to have lower hardness. Prior art metal materials and fluororesins fail to meet such requirements, and rolls of the type in which fluororesin is coated over heat conductive silicone rubber are often employed. In particular, the rubber used in heating rolls is required to have a high thermal conductivity from the standpoints of reducing the waiting time upon startup of the machine and saving the energy consumed by the machine itself. A low compression set is also required because the rubber is always exposed to high temperatures of 150 to 200° C. However, since silicone rubber itself is not so heat conductive, fillers having a high thermal conductivity are generally added. Such filled silicone rubber compositions are disclosed, for example, in JP-A 58-219259 corresponding to U.S. Pat. No. 4,444,944, JP-A 3-221982 and JP-A 10-39666. In these compositions, silica, alumina, magnesium oxide and the like are added to common silicone rubbers as the heat conductive filler. These fillers, however, have the problem that when heavily loaded, they are detrimental to silicone rubber at elevated temperature. JP-A 63-251466 corresponding to U.S. Pat. No. 5,008,307 describes that alumina having alkali and acid levels of up to 5 ppm is recommended for electronic part application, but does not refer to the pH of alumina itself. When alumina is removed of alkali and acid components as by washing, the resulting filler becomes expensive. This patent refers nowhere to the application to rolls and belts. JP-A 11-116806 describes that the use of alumina containing a reduced sodium level of up to 50 ppm contributes to improved heat resistance. No reference is made to the pH of alumina itself nor the use of fillers having different pH. JP-A 2002-72728 corresponding to U.S. Pat. No. 6,569,536 discloses the use of alumina having a reduced heat loss although this does not achieve satisfactory results.